Method for determining preferential deposition parameters for a thin layer of iii-v material

ABSTRACT

First, second and third series of samples are successively made so as to determine the influence of the deposition parameters on the crystallographic quality of a layer of semiconductor material of III-V type. The parameters studied are successively the deposition pressure, the deposition temperature and the deposited thickness of a sub-layer of semiconductor material of III-V type so as to respectively determine a first deposition pressure, a first deposition temperature at the first deposition pressure, and a first deposited thickness at the first deposition temperature and at the first deposition pressure. The sub-layer of semiconductor material of III-V type is thickened by ways of a second layer of semiconductor material of III-V type deposited under different conditions.

BACKGROUND OF THE INVENTION

The invention relates to a method for determining deposition parametersof a layer made from semiconductor material of III-V type on a germaniumlayer.

State of the Art

For a large number of years, semiconductor materials of III-V type suchas GaAs, InP and their associated alloys have enabled a considerablebreakthrough to be made in optoelectronics. These materials have enableddevices with very good performances to be produced in the field of laserdiodes and light-emitting diodes.

However, commonplace use of semiconductor materials of III-V type islimited by the difficulties of integration of these materials in modernmicroelectronic circuits which are for the most part fabricated onsilicon substrates. The very large lattice parameter difference whichexists between semiconductor materials of III-V type and silicon makesintegration of an optoelectronic module on a silicon substrate extremelydifficult to achieve.

Heteroepitaxy of GaAs layers on silicon substrates has been the subjectof a great deal of research over the last few years. The publication byKawabe et al. “Molecular Beam Epitaxy of Controlled Single Domain GaAsOn Si (100)”, Japanese Journal of Applied Physics, Part 2: Letters,25(4), pp. 285-287 (1986) describes epitaxial growth of a GaAs layerdirectly on a silicon substrate. Growth is performed by the molecularbeam epitaxy technique. This document teaches that the use of a siliconsurface misaligned along the <110> axis enables the antiphase boundariesto be eliminated (misalignment of 4°+/−1°).

However, silicon substrates misaligned by few degrees are hardlycompatible with the microelectronics industry. It is therefore verydifficult to use this teaching for industrial fabrication of integratedcircuits associated with optoelectronic modules formed fromsemiconductor material of III-V type.

The publication by Sieg et al. “Anti-Phase Domain-Free Growth of GaAs onOffcut (001) Ge wafers by Molecular Beam Epitaxy with Suppressed GeOutdiffusion”, Journal of Electronics Materials 27(7), pp. 900-907(1998) describes epitaxial growth of a GaAs layer directly on agermanium substrate. The lattice parameter of germanium is quite closeto the lattice parameter of the GaAs Crystal. This document teaches thatthe use of a germanium surface of (001) type misaligned in the <110>direction enables the anti-phase boundaries to be eliminated. Hereagain, it is important to observe that germanium substrates aredifficult to use to form integrated circuits.

The publication by Chriqui “Direct Growth of GaAs-based structures onexactly (001)-oriented Ge/Si virtual substrates: reduction of thestructural defect density and observation of electroluminescence at roomtemperature under CW electrical injection”, Journal of Crystal Growth265, pp 53-59 (2004) describes growth of a GaAs layer on a germaniumlayer itself formed on a silicon substrate. Growth is performed byepitaxy in vapor phase by means of organometallic precursors. Differentsamples were produced and studied. This document describes a sample inwhich a buffer layer of GaAs is covered by another layer of GaAs. Undera first condition, growth of the GaAs layer is performed at atemperature equal to 650° C. The presence of holes in the GaAs layers isobserved. Growth at 450° C. is also performed and the layer formed nolonger presents any holes.

The publication by Xuliang Zhou et al (Journal of Semiconductors, vol.35, no. 7, page 073002 July 2014) deals with GaAs epitaxy with a lowdefect density and a smooth surface on a silicon substrate and proposesoptimising the growth of GaAs thin films on misaligned Ge. Differentdeposition conditions are presented for deposition of the germaniumbuffer layer or for the deposited thickness of GaAs film. The substrateused is a substrate of (100) type misaligned by 5° with respect to the[110] direction.

The publication by Ngoc Duy Nguyen (ECS Transactions, vol. 33, no. 6,pages 933-939 January 2010) deals with GaAs epitaxy on a Ge layer. Alayer of Ge with a thickness of 1 μm is deposited on a silicon layer.The Ge layer is polished by CMP before deposition of a GaAs layer. Thesubstrate is a substrate of (100) type misaligned by 6° with respect tothe <110> direction.

The document WO 2005/108654 describes a fabrication method of a virtualsubstrate for integration of III/V materials on silicon. The siliconsubstrate is successively capped by a layer of germanium and then by twolayers of GaAs. The substrate is a substrate of (100) type misaligned by6° with respect to the <110> direction.

OBJECT OF THE INVENTION

The object of the invention is to present a method for determiningdeposition conditions of a first layer of semiconductor material ofIII-V type on a germanium layer that is easy to implement and enablesthe conditions ensuring deposition of good crystallographic quality tobe defined quickly.

This result tends to be achieved by means of a method for determiningdeposition parameters of a first layer of semiconductor material ofIII-V type in a sample successively comprising:

-   -   a monocrystalline layer of relaxed germanium epitaxially grown        from a first surface of crystalline orientation of (001) type of        a monocrystalline silicon layer,    -   a first monocrystalline layer made from semiconductor material        of III-V type,    -   a second monocrystalline layer made from semiconductor material        of III-V type, the stack formed by the first and second layers        of semiconductor material of III-V type having a thickness E,

the method comprising:

-   -   making a first series of samples in which the first layer of        semiconductor material of III-V type having a first thickness is        covered by the second layer of semiconductor material having a        second thickness, the deposition conditions of the first layer        of semiconductor material of III-V type being chosen such that        the deposition pressure differs between the samples, the        deposition temperature being identical between the samples and        equal to a first deposition temperature,    -   determining a first deposition pressure from the first series of        samples and at least from a first parameter representative of        the crystalline quality of the stack formed by the first and        second layers of semiconductor material of III-V type,    -   making a second series of samples in which the first layer of        semiconductor material of III-V type having the first thickness        is covered by the second layer of semiconductor material of        III-V type having the second thickness, the deposition        conditions of the first layer of semiconductor material of III-V        type being chosen such that the deposition temperature differs        between the samples, the deposition pressure being identical        between the samples and equal to the first deposition pressure,    -   determining a second deposition temperature from the second        series of samples and by means of a second parameter        representative of the crystalline quality of the stack formed by        the first and second layers of semiconductor material of III-V        type.

In an alternative embodiment, the order of the steps is changed so thatthe method comprises on the samples described in the foregoing:

-   -   making a first series of samples in which the first layer of        semiconductor material of III-V type having a first thickness is        covered by the second layer of semiconductor material having a        second thickness, the deposition conditions of the first layer        of semiconductor material of III-V type being chosen such that        the deposition temperature differs between the samples, the        deposition pressure being identical between the samples and        equal to an initial deposition pressure,    -   determining a first deposition temperature from the first series        of samples and by means of at least a first parameter        representative of the crystalline quality of the stack formed by        the first and second layers of semiconductor material of III-V        type,    -   making a second series of samples in which the first layer of        semiconductor material of III-V type having the first thickness        is covered by the second layer of semiconductor material of        III-V type having the second thickness, the deposition        conditions of the first layer of semiconductor material of III-V        type being chosen such that the deposition pressure differs        between the samples, the deposition temperature being identical        between the samples and equal to the first deposition        temperature,    -   determining a first deposition pressure from the second series        of samples and by means of a second parameter representative of        the crystalline quality of the stack formed by the first and        second layers of semiconductor material of III-V type.

In an alternative embodiment, the method further comprises:

-   -   making a third series of samples in which the first layer of        semiconductor material of III-V type is covered by this second        layer of semiconductor material of III-V type, the thickness of        the stack formed by the first and second layers being equal to        the thickness E, the deposition conditions of the first layer of        semiconductor material of III-V type being chosen such that the        deposited thickness differs between the samples, the deposition        pressure being identical between the samples and equal to the        first deposition pressure, the deposition temperature being        equal between the samples and equal to the second deposition        temperature,    -   determining a third deposition thickness of the first layer of        semiconductor material of III-V type from the third series of        samples by means of a third parameter representative of the        crystalline quality of the stack formed by the first and second        layers of semiconductor material of III-V type.

In a preferred embodiment, the second layer of semiconductor material ofIII-V type is deposited at a pressure equal to 20 Torr and at atemperature equal to 615° C.

It is also advantageous to provide for the first thickness of the firstlayer of semiconductor material of III-V type to be comprised between 10nm and 80 nm and more particularly between 15 nm and 50 nm and even moreparticularly between 20 and 40 nm.

In a particular embodiment, it is advantageous to provide for the firstdeposition temperature to be comprised between 400° C. and 650° C., andpreferentially between 495° C. and 615° C. and even more preferentiallybetween 500° C. and 550° C. and in particularly advantageous mannerbetween 515° C. and 540° C.

To form the germanium layer, it is advantageous to provide for therelaxed germanium monocrystalline layer to be epitaxially grown from afirst surface of crystalline orientation of (001) type of amonocrystalline silicon layer. In a particularly advantageousconfiguration, the monocrystalline germanium layer is produced by meansof a first deposition of a first germanium layer at a temperature ofless than 500° C. followed by a second deposition of a second germaniumlayer at a temperature of more than 500° C.

It is also advantageous to provide a semiconductor material of III-Vtype chosen from GaAs, InP and the following ternary alloys: AlGaAs,InGaAs with an indium concentration less than or equal to 10%.

To easily choose an advantageous deposition pressure, it is advantageousto choose that the first parameter be a curve break in a curverepresentative of the defect density visible by optic microscopyaccording to the deposition pressure.

To easily choose an advantageous deposition temperature, it isadvantageous to choose that the second parameter be an extremum in acurve representative of the defect density visible by optic microscopyaccording to the deposition temperature.

To easily choose an advantageous deposition thickness, it isadvantageous to choose that the third parameter be an extremum in acurve representative of the defect density visible by optic microscopyaccording to the thickness of the first layer of semiconductor materialof III-V type.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from thefollowing description of particular embodiments of the invention givenfor non-restrictive example purposes only and represented in theappended drawings, in which:

FIGS. 1 and 2 represent a stack of layers used for fabrication of asample, in schematic manner in cross-section,

FIG. 3 represents a sequencing of steps for making a sample, inschematic manner,

FIG. 4 represents a sequencing of steps for determining the improveddeposition parameters, in schematic manner.

DETAILED DESCRIPTION

As illustrated in FIG. 1, a silicon layer 1 is provided covered by agermanium layer 2. The silicon layer 1 presents a thicknessadvantageously comprised between 150 μm and 1000 μm. The silicon layer 1can form a substrate or be deposited on the substrate. The diameter ofthe substrate is advantageously greater than or equal to 100 mm. Thediameter of the substrate is for example equal to 100 mm, 200 mm or 300mm so as to be used by conventional microelectronics industry equipment.

The silicon layer 1 has a first surface the crystalline orientation ofwhich is preferably of (001) type so as to be compatible withconventional fabrication methods of microelectronic chips and moreparticularly of field effect transistors, for example of MOS type. Thecrystalline orientation is of (001) type, i.e. the first surfacepresents a misalignment of less than 1° with respect to the (001) plane.The method is particularly advantageous as it enables optimal operatingconditions to be encountered for substrates of (001) type which are onlyslightly misaligned or not misaligned which is innovating with respectto the teachings of the prior art where the substrates are greatlymisaligned (a misalignment typically more than 5°).

The silicon layer 1 has a first surface which is partially covered or atleast partially covered by the germanium layer 2. As a variant, thesilicon layer 1 can be eliminated, and the germanium layer acts assupport. A germanium substrate can be used.

As illustrated in FIG. 3, the substrate can be produced by means of thefollowing steps. A substrate comprising the silicon layer 1 is providedin a step F1. A germanium layer 2 is epitaxially grown on the siliconlayer 1 in a step F2.

The germanium layer 2 is preferentially monocrystalline. The germaniumlayer 2 presents a thickness which is advantageously comprised between0.1 μm and 10 μm. The germanium layer 2 is at least partially relaxed sothat the lattice parameter at the surface of the layer 2 is equal orsubstantially equal to that of the germanium crystal. What is meant bygermanium layer is one or more layers of germanium or ofsilicon-germanium alloy the atomic concentration of germanium of whichis at least equal to 70%. The set of layers forming the germanium layer2 presents a total thickness advantageously comprised in the rangeindicated in the foregoing. Advantageously, the top part of thegermanium layer 2, i.e. the part designed to be in contact with thelayer of semiconductor material 3 of III-V type, is made from puregermanium or from silicon-germanium alloy so that the top part of thegermanium layer 2 presents the same lattice parameter as relaxedgermanium.

The germanium layer 2 can be deposited by any suitable technique, forexample by means of molecular beam epitaxy or by chemical vapordeposition.

In an advantageous embodiment illustrated in FIG. 2, the germanium layer2 is produced by means of two successive deposition steps of a germaniumlayer, preferably made from pure germanium. A first deposition step F2 ais performed with a deposition temperature of less than 500° C. to forma first germanium layer 2 a. A second germanium deposition step F2 b isthen performed at a temperature of more than 500° C. to form a secondgermanium layer 2 b. A first germanium layer 2 a is thus formed at atemperature of less than 500° C., advantageously between 350° C. and450° C., and a second germanium layer 2 b is formed on the first layer 2a. The second germanium layer 2 b is formed at a temperature of morethan 500° C., advantageously between 600° C. and 750° C. The use of ahigh temperature to form the second germanium layer enables thedeposition time to be reduced when large thicknesses have to bedeposited.

This breakdown into two consecutive deposition steps F2 a and F2 b makesit possible to have a surface of better quality for the future growth ofthe layer 3 of semiconductor material of III-V type.

In the case of deposition of the layer 1 on a silicon substrate, the useof a first deposition temperature which is relatively low enables thelattice parameter mismatch between the silicon and the layer 2 a to beaccommodated while ensuring formation of a smooth layer 2 a. The use ofhigher temperatures for growth of the layer 2 b then enables the surfaceroughness and defect density to be reduced.

In advantageous manner, the substrate remains in the same depositionchamber for growth of the layers 2 a and 2 b without being extractedinto an outside environment.

In advantageous manner, thermal annealing is performed on the stack ofthe first layer 2 a and second layer 2 b of germanium in a step F3. Thisannealing enables the strains in the germanium layers to be reduced andfacilitates relaxation of the germanium layer. Annealing isadvantageously performed at a temperature comprised between 800° C. and900° C., preferentially at 850° C. In advantageous manner, the heattreatment time at a temperature of more than 800° C. is about a fewminutes, preferably between 1 and 10 minutes. In a particularembodiment, the annealing is performed by means of a plateau at apredefined temperature which advantageously represents the maximumannealing temperature. In an alternative embodiment, the annealing isperformed by means of several different temperatures appliedconsecutively. In preferential manner, the annealing comprises analternation between a high temperature and a low temperature so that theannealing alternates the temperature increase periods and thetemperature decrease periods. In advantageous manner, the annealingcomprises between 3 and 4 temperature cycles, a cycle comprising atemperature increase and a temperature decrease. In an advantageousembodiment, a cycle also comprises a temperature plateau for a timepreferably comprised between 1 and 30 seconds. The high temperature isadvantageously comprised between 800° C. and 900° C. and/or in thetemperature range comprised between the growth temperature of the layer2 b +20° C., and the growth temperature of the layer 2 b −20° C. In oneembodiment, the low temperature can also can be comprised between 800°C. and 900° C.

In an alternative embodiment which can be combined with the previousembodiments, a chemical mechanical polishing step F4 is performed on thesurface of the germanium layer 2 or 2 b. In this way, it is possible toform a germanium layer 2/2 b having a surface which presents similarproperties to a germanium substrate. However, it was unexpectedlyobserved that very good results are able to be obtained without the useof the chemical mechanical polishing step.

For example purposes, the pure germanium layer 2 is achieved by means ofa first deposition at a temperature of less than 500° C. and a seconddeposition at a temperature of more than 500° C. The stack is subjectedto thermal annealing. With these operating conditions, it was possibleto produce a pure germanium layer having a surface lattice parameteridentical to that of the germanium crystal to within 0.5%. The measuredlattice parameter is comprised between 5.63 Å and 5.69 Å. At the surfaceof the germanium layer, the roughness was measured as being less than 1nm (rms roughness-rms standing for root mean square) on a 1×1 μm² field.

A layer of semiconductor material of III-V type is then deposited on thegermanium layer 2 by metalorganic chemical vapor deposition (MOCVD). Ina particularly advantageous manner, the layer of semiconductor materialof III-V type is broken down into two elementary layers called firstlayer of semiconductor material 3 of III-V type and second layer ofsemiconductor material 4 of III-V type. Layers 3 and 4 are deposited intwo distinct steps F5 and F6 with different deposition parameters, forexample different deposition pressures and/or deposition temperatures.

The second layer of semiconductor material 4 of III-V type is separatedfrom the germanium layer 2 by the first layer of semiconductor material3 of III-V type as can be seen in FIGS. 1 and 2.

What is meant by semiconductor material of III-V type is a material suchas GaAs, InP and the following ternary alloys: AlGaAs, InGaAs with anindium concentration less than or equal to 10%. In general manner, thesemiconductor material of III-V type is a material which presents alattice parameter in the 5.39 Å-5.63 Å range.

The deposited first layer of semiconductor material 3 of III-V type isassimilated to a nucleation layer. These deposition conditions arechosen such that the layer 3 of III-V material covers a maximum of thesurface of the germanium layer 2.

Deposition of the first layer 3 is followed by deposition of the secondlayer 4 of semiconductor material of III-V type. The operatingconditions are different and are chosen so as to achieve thickening ofthe first layer 3. For example, deposition of the second layer 4 isperformed at a total pressure equal to 20 Torr. This deposition pressureenables a thickening of good quality to be had from the first layer 3.The pressure of 20 Torr ensures a good uniformity of deposition inaddition to growth of a material of good crystallographic quality.

For example, a second layer 4 of GaAs can be deposited under thefollowing conditions by organometallic chemical vapor deposition:

Pressure: 20 Torr (1 pascal=0.0075006 Torr)

Temperature: 615° C.

Organometallic precursors: Tributhylarsenic and Tributhylgallium.

In addition to breaking down deposition of the layer of semiconductormaterial of III-V type into two distinct deposition phases, it wasdiscovered that particularly advantageous operating conditions exist fordeposition of the first layer 3 of semiconductor material of III-V type.A quick and efficient manner for achieving these optimal or almostoptimal deposition conditions was also discovered.

In a step F7, a first set of samples is produced. For each of thesamples of the first set, two successive layers of semiconductormaterial of III-V type are deposited, layers 3 and 4. The first layer 3of semiconductor material of III-V type is deposited with differentdeposition parameters so as to seek to ascertain the influence of thedeposition pressure on the crystallographic quality of the stack ofsemiconductor material of III-V type formed by layers 3 and 4. Thedeposited thickness of the first layer 3 of semiconductor material ofIII-V type is constant between the samples of the first set. Thedeposition temperature is constant between the samples of the first setand equal to an initial deposition temperature.

The second layer of semiconductor material of III-V type is depositedunder similar conditions for all the samples (thickness, temperature,pressure).

Once the first series of samples has been made, the latter are analysedso as to determine the influence of the deposition pressure on at leastone of the parameters representative of the crystallographic quality ofthe deposition. In a step F8, this analysis enables a first depositionpressure P₀ to be determined which is the optimal deposition pressure ora pressure close to the optimal deposition pressure to obtain adeposition having a good crystallographic quality.

A first parameter is used so as to determine the pressure P₀. The firstparameter is representative of the crystallographic quality of theassembly formed by layers 3 and 4. In the following examples, theparameter used is a defect density observed in top view by means of anoptic microscope in Nomarski mode. In preferential manner, the firstparameter is a slope break or a mimima in a curve representative of thedensity of optically visible defects versus the deposition pressure. Theslope break can be a difference of at least 10% in the slopes of thesegments, preferably at least 20% or at least 30%.

Sample 1

The first GaAs layer 3 was deposited at the pressure of 20 Torr and witha deposition temperature equal to 615° C. The organometallic precursorsare Tributhylarsenic and Tributhylgallium. The thickness of the firstGaAs layer 3 is equal to 80 nm and was thickened by means of the secondGaAs layer 4 so that the thickness of the stack is equal to 270 nm.

Observation by optic microscope in Nomarski mode enabled a large densityof holes to be observed making the surface of the sample very rough withan enlargement of ×50. On the observed samples, the hole density isgreater than 10⁸/cm².

Sample 2

The first GaAs layer 3 was deposited at a pressure of 80 Torr and with adeposition temperature equal to 615° C. The organometallic precursorsare Tributhylarsenic and Tributhylgallium. The thickness of the firstGaAs layer 3 is equal to 80 nm and it was thickened by means of thesecond GaAs layer 4 so that the thickness of the stack is equal to 270nm.

Observation by optic microscope in Nomarski mode (under the sameconditions as previously) enabled a low hole density to be observedmaking the surface of the sample more easily usable than example 1. Onthe observed samples, the hole density is equal to 10⁷/cm².

Sample 3

The first GaAs layer 3 was deposited at a pressure of 450 Torr and witha deposition temperature equal to 615° C. The organometallic precursorsare Tributhylarsenic and Tributhylgallium. The thickness of the firstGaAs layer 3 is equal to 80 nm and it was thickened by means of thesecond GaAs layer 4 so that the thickness of the stack is equal to 270nm.

Observation by optic microscope in Nomarski mode did not enable anyholes to be observed. The surface appears to be very smooth. However, alarge non-uniformity was observed in the deposited thickness of thefirst GaAs layer. On the observed samples, the hole density is equal to10⁷/cm².

The non-uniformity of the thickness of the first GaAs layer 3 means thatdeposition at the pressure of 450 Torr is unusable in industrial manner.The thickness measurements made on the first GaAs layer 3 do in factshow that in the centre of the substrate the deposited thickness is lessthan 5 nm whereas at the periphery of the substrate the depositedthickness is substantially equal to 45 nm.

In the above sample, measurement of the hole density by observation withan optic microscope in Nomarski mode makes it possible to differentiatebetween depositions having a good crystallographic quality anddepositions having an unacceptable crystallographic quality. However, itis also apparent in the foregoing example that the hole densitycriterion alone is not always sufficient and that it is advantageous tocombine it with a criterion on the uniformity of deposition.

For example, the criterion on the non-uniformity NU can be calculated inthe following manner:

NU=(Emax−Emin)/Emean

Emax represents the maximum measured thickness

Emin represents the minimum measured thickness

Emean represents the mean value of the measurements.

In advantageous manner, 49 uniformly distributed measurements are madeon the substrate excluding the 5 mm of the outer edge of the substrate.

If the NU criterion has a value of less than 0.1, the deposition isconsidered as being uniform.

In a step F9, a second set of samples is made so as to investigate theinfluence of the deposition temperature on the crystallographic qualityof the semiconductor material of III-V type.

For each of the samples of the second set, two successive layers ofsemiconductor material of III-V type are deposited. The first layer 3 ofsemiconductor material of III-V type is deposited with differentparameters so as to seek to ascertain the influence of the depositiontemperature on the crystallographic quality of the semiconductormaterial of III-V type. The deposited thickness of the first layer 3 ofsemiconductor material of III-V type is constant between the samples ofthe second set. The deposition pressure is constant between the samplesof the second set and is equal to the first deposition pressure P₀determined beforehand.

The second layer 4 of semiconductor material of III-V type is depositedunder similar conditions for all the samples (thickness, temperature,pressure). The conditions are advantageously similar to those of thefirst series of samples.

Once the second series of samples has been made, the latter are analysedso as to determine the influence of the deposition temperature on atleast one of the parameters representative of the crystallographicquality of the deposition. In a step F10, this analysis enables a firstdeposition temperature T₀ to be determined, which is the optimaldeposition temperature or a temperature close to the optimal depositiontemperature at the first deposition pressure P₀. The analysis isperformed by means of a second parameter which can be identical to ordifferent from the first parameter representative of thecrystallographic quality used to quantify the influence of thedeposition pressure.

It would appear detrimental to perform deposition of the layer ofsemiconductor material III-V and more particularly of GaAs at atemperature of more than 700° C., as in this temperature range, theorganometallic precursors decompose in gaseous phase to form sub-specieswhich are very difficult to incorporate in the semiconductor layers. Itis therefore advantageous to limit the range of study to a maximumdeposition temperature of less than 700° C. and preferentially less than650° C. It seems advantageous to limit the range of study to atemperature less than or equal to 400° C. in order not to get draggedinto too long methods which are therefore unsuitable for an industrialuse.

For example, samples are formed with deposition temperatures comprisedbetween 495° C. and 615° C. It is apparent that from 615° C., areduction of the deposition temperature enables the quality of the GaAslayers to be improved by reducing the observable hole density. However,it was also observed that below 500° C., the defect density observed inthe GaAs layers increases. For a first deposition pressure P₀, anoptimal deposition temperature exists which is not necessarily theminimum temperature accessible by the deposition equipment. For severalthickness conditions, it seems advantageous to limit the range of studyto the 500-550° C. range or even to the 515-54020 C. range, as thedecision criterion is observed in these temperature ranges. It isadvantageous to choose the initial deposition temperature in one of theabove ranges.

The different samples were observed under the same conditions as beforeand the following defect densities were measured.

585° C., the defect density is equal to 1.10⁷ cm⁻²

555° C., the defect density is equal to 1.10⁷ cm⁻²

525° C., the defect density is equal to 1.10⁶ cm⁻²

495° C., the defect density is equal to 2.10⁶ cm⁻²

For example, the second parameter enabling the first depositiontemperature to be determined is the defect density observed by opticmicroscopy in Nomarski mode and more particularly the minimum of thecurve representing the defect density versus the temperature. Thissecond discrimination parameter can be generalised to other materialsthan GaAs, for example to all semiconductor materials of III-V type.

Then, in a step F11, a third series of samples is made. For each of thesamples of the third set, two successive layers of semiconductormaterial of III-V type are deposited. The first layer 3 of semiconductormaterial of III-V type is deposited at the first deposition temperatureT₀ and at the first deposition pressure P₀. Only the deposited thicknessvaries between the samples so as to seek to ascertain the influence ofthe deposited thickness of the first layer 3 on the crystallographicquality of the final semiconductor material of III-V type. The depositedthickness of the stack formed by the first and second layers ofsemiconductor material of III-V type is constant between the samples ofthe third set.

The second layer 4 of semiconductor material of III-V type is depositedunder similar conditions for all the samples (temperature and pressure)but with a variable thickness.

Once the third set of samples has been made, the latter are analysed soas to determine the influence of the thickness of the first layer 3 onat least one of the parameters representative of the crystallographicquality of the total deposition. This analysis enables a thirddeposition thickness to be determined for the first layer. This analysisis performed by means of a third parameter which can be different fromthe first and second parameters. It can also be envisaged that the thirdparameter be identical to the first and/or second parameters usedbeforehand.

For example, for a deposition of GaAs of a total thickness of 270 nm,the protocol described in the foregoing makes it possible to rapidlydetermine that it is preferable to deposit a first layer of GaAs at apressure P₀ equal to 80 Torr, with a temperature T₀ equal to 525° C. anda thickness of the first layer 3 comprised between 20 nm and 40 nm.

As indicated in the foregoing, the GaAs layer is broken down into afirst nucleation layer and a second thickening layer. These two layersare fabricated with different operating conditions. The second layer 2 bis not advantageous to form the whole of layer 2 as it does not enablelow defect densities to be obtained. It is therefore advantageous todissociate the layer 2 into a layer 2 a, followed by a layer 2 b.

In the foregoing exemplary embodiments, the organometallic precursorsare Tributhylarsenic and Tributhylgallium. It is however possible to useother organometallic precursors, for example triethylgallium ortrimethygallium. It is further possible to use precursors of hydridetype, for example arsine (AsH3) for arsenic.

Although the above examples present deposition of GaAs on a germaniumlayer, it is possible to use this fabrication method for deposition of alayer of InP on a germanium layer which may itself be formed on asilicon substrate.

In an advantageous embodiment, the thickness of the first layer 3 isfixed to a value comprised between 20 nm and 40 nm. In this exemplarycase, the third series of samples is not made which enables time to besaved while achieving an interesting result. It is neverthelessadvantageous to make the third series of samples to obtain an optimalresult.

In an alternative embodiment, the second series of samples is madebefore the first series of samples in order to fix the depositiontemperature before defining the deposition pressure. This embodimentalso enables a satisfactory operating point to be found. However, thisoperating point is different from the previously described operatingpoint and it is apparent that the deposition rates obtained are lower.This variant therefore seems to be less advantageous. For example, inthis alternative embodiment, the optimal deposition temperature waschosen equal to 375° C. Then the deposition pressure was chosen equal to450 Torr. The optimal thickness of the first layer 3 was chosen equal to30 nm.

In this embodiment, a first set of samples is made (F7) in which thefirst layer of semiconductor material (3) of III-V type having a firstthickness is covered by the second layer of semiconductor material (4)having a second thickness. The deposition conditions of the first layerof semiconductor material (3) of III-V type are chosen such that thedeposition temperature differs between the samples. The depositionpressure is identical between the samples and equal to an initialdeposition pressure.

A first deposition temperature (T₀) is then determined (F8) from thefirst series of samples and by means of at least one first parameterrepresentative of the crystalline quality of the stack formed by thefirst and second layers of semiconductor material (3, 4) of III-V type.

A second series of samples is made (F9) in which the first layer ofsemiconductor material (3) of III-V type having the first thickness iscovered by the second layer of semiconductor material (4) of III-V typehaving the second thickness. The deposition conditions of the firstlayer of semiconductor material (3) of III-V type are chosen such thatthe deposition pressure differs between the samples. The depositiontemperature is identical between the samples and equal to the firstdeposition temperature (T₀).

A first deposition pressure (P₀) is then determined (F10) from thesecond series of samples and by means of the second parameterrepresentative of the crystalline quality of the stack formed by thefirst and second layers of semiconductor material (3, 4) of III-V type.

1. A method for determining deposition parameters of a first layer madefrom semiconductor material of III-V type in a sample successivelycomprising: a monocrystalline layer of relaxed germanium epitaxiallygrown from a first surface of crystalline orientation of (001) type of amonocrystalline silicon layer, a first monocrystalline layer made fromsemiconductor material of III-V type formed by organometallic chemicalvapor deposition, a second monocrystalline layer made from semiconductormaterial of III-V type formed by organometallic chemical vapordeposition, the stack formed by the first and second monocrystallinelayers of semiconductor material of III-V type having a thickness E, themethod comprising: making a first series of samples in which the firstlayer of semiconductor material of III-V type having a first thicknessis covered by the second layer of semiconductor material having a secondthickness, the deposition conditions of the first layer of semiconductormaterial of III-V type being chosen such that the deposition pressurediffers between the samples of the first series, the depositiontemperature being identical between the samples of the first series andequal to an initial deposition temperature, determining a firstdeposition pressure from the first series of samples and by means of atleast a first parameter representative of a crystalline quality of thestack formed by the first and second monocrystalline layers ofsemiconductor material of III-V type, making a second series of samplesin which the first layer of semiconductor material of III-V type havingthe first thickness is covered by the second layer of semiconductormaterial of III-V type having the second thickness, the depositionconditions of the first layer of semiconductor material of III-V typebeing chosen such that the deposition temperature differs between thesamples of the second series, the deposition pressure being identicalbetween the samples of the second series and equal to the firstdeposition pressure, determining a first deposition temperature from thesecond series of samples and by means of a second parameterrepresentative of the crystalline quality of the stack formed by thefirst and second monocrystalline layers of semiconductor material ofIII-V type.
 2. A method for determining deposition parameters of a firstlayer made from semiconductor material of III-V type in a samplesuccessively comprising: a monocrystalline layer of relaxed germaniumepitaxially grown from a first surface of crystalline orientation of(001) type of a monocrystalline silicon layer, a first monocrystallinelayer made from semiconductor material of III-V type formed byorganometallic chemical vapor deposition, a second monocrystalline layermade from semiconductor material of III-V type formed by organometallicchemical vapor deposition, the stack formed by the first and secondmonocrystalline layers of semiconductor material of III-V type having athickness E, the method comprising: making a first series of samples inwhich the first layer of semiconductor material of III-V type having afirst thickness is covered by the second layer of semiconductor materialhaving a second thickness, the deposition conditions of the first layerof semiconductor material of III-V type being chosen such that thedeposition temperature differs between the samples of the first series,the deposition pressure being identical between the samples of the firstseries and equal to an initial deposition pressure, determining a firstdeposition temperature from the first series of samples and by means ofat least a first parameter representative of the crystalline quality ofthe stack formed by the first and second monocrystalline layers ofsemiconductor material of III-V type, making a second series of samplesin which the first layer of semiconductor material of III-V type havingthe first thickness is covered by the second layer of semiconductormaterial of III-V type having the second thickness, the depositionconditions of the first layer of semiconductor material of III-V typebeing chosen such that the deposition pressure differs between thesamples of the second series, the deposition temperature being identicalbetween the samples of the second series and equal to the firstdeposition temperature, determining a first deposition pressure from thesecond series of samples and by means of a second parameterrepresentative of the crystalline quality of the stack formed by thefirst and second monocrystalline layers of semiconductor material ofIII-V type.
 3. The method for determining according to claim 1,comprising: making a third series of samples in which the first layer ofsemiconductor material of III-V type is covered by the second layer ofsemiconductor material of III-V type, the thickness of the stack formedby the first and second monocrystalline layers of semiconductor materialof III-V type being equal to the thickness E, the deposition conditionsof the first layer of semiconductor material of III-V type being chosensuch that the deposited thickness differs between the samples of thethird series, the deposition pressure being identical between thesamples of the third series and equal to the first deposition pressure,the deposition temperature being equal between the samples of the thirdseries and equal to the first deposition temperature, determining athird deposition thickness of the first layer of semiconductor materialof III-V type from the third series of samples by means of a thirdparameter representative of the crystalline quality of the stack formedby the first and second monocrystalline layers of semiconductor materialof III-V type.
 4. The method for determining according to claim 1,wherein the second layer of semiconductor material of III-V type isdeposited at a pressure equal to 20 Torr and at a temperature equal to615° C.
 5. The method for determining according to claim 1, wherein thefirst thickness of the first layer of semiconductor material of III-Vtype is comprised between 10 nm and 80 nm.
 6. The method for determiningaccording to claim 5, wherein the first thickness of the first layer ofsemiconductor material of III-V type is comprised between 15 nm and 50nm.
 7. The method for determining according to claim 6, wherein thefirst thickness of the first layer of semiconductor material of III-Vtype is comprised between 20 and 40 nm.
 8. The method for determiningaccording to claim 1, wherein the initial deposition temperature iscomprised between 400° C. and 650° C.
 9. The method for determiningaccording to claim 8, wherein the initial deposition temperature iscomprised between 495° C. and 615° C.
 10. The method for determiningaccording to claim 9, wherein the initial deposition temperature iscomprised between 500° C. and 550° C.
 11. The method for determiningaccording to claim 10, wherein the initial deposition temperature iscomprised between 515° C. and 540° C.
 12. The method for determiningaccording to claim 1, wherein the monocrystalline germanium layer isproduced by means of a first deposition of a first germanium layer at atemperature of less than 500° C. followed by a second deposition of asecond germanium layer at a temperature of more than 500° C.
 13. Themethod for determining according to claim 1, wherein the semiconductormaterial of III-V type is chosen from GaAs, InP and the followingternary alloys: AlGaAs, InGaAs with an indium concentration less than orequal to 10%.
 14. The method for determining according to claim 1,wherein the first parameter is a slope break in a curve representativeof a defect density visible by optic microscopic according to thedeposition pressure.
 15. The method for determining according to claim1, wherein the second parameter is an extremum in a curve representativeof a defect density visible by optic microscopic according to thedeposition temperature.
 16. The method for determining according toclaim 3, wherein the third parameter is an extremum in a curverepresentative of a defect density visible by optic microscopicaccording to the thickness of the first layer of semiconductor materialof III-V type.
 17. The method for determining according to claim 2,comprising: making a third series of samples in which the first layer ofsemiconductor material of III-V type is covered by the second layer ofsemiconductor material of III-V type, the thickness of the stack formedby the first and second layers of semiconductor material of III-V typebeing equal to the thickness E, the deposition conditions of the firstlayer of semiconductor material of III-V type being chosen such that thedeposited thickness differs between the samples of the third series, thedeposition pressure being identical between the samples of the thirdseries and equal to the first deposition pressure, the depositiontemperature being equal between the samples of the third series andequal to the first deposition temperature, determining a thirddeposition thickness of the first layer of semiconductor material ofIII-V type from the first series of samples by means of a thirdparameter representative of the crystalline quality of the stack formedby the first and second monocrystalline layers of semiconductor materialof III-V type.
 18. The method for determining according to claim 2,wherein the second layer of semiconductor material of III-V type isdeposited at a pressure equal to 20 Torr and at a temperature equal to615° C.
 19. The method for determining according to claim 2, wherein thefirst thickness of the first layer of semiconductor material of III-Vtype is comprised between 10 nm and 80 nm.